Position input systems, also known as pen tablets or tablet/digitizers, have seen widespread use as input devices for computers, for example. The position input system generally comprises a pen-type or stylus-type position indicator (also referred to herein as a position pointing device) for indicating a position on a tablet, and a position detection device. In such a position input system signals transmitted from the position indicator are received by the position detection device to detect the position on the tablet indicated by the position indicator. So far various technologies have been developed for detecting the position designated on the tablet. Of these various kinds of developed technologies, an electromagnetic induction system position detecting apparatus like the invention described in Japanese Published Patent Application No. 2-53805 is known for detecting the position designated on the tablet.
In recent years, position input systems have appeared which are integrated with a liquid crystal display device, and which enable operation of the position indicator on a display screen. Generally in such a position input system, electric waves are transmitted to the position indicator from the position detector device integrated with the display screen, and these electric waves are utilized to transmit signals from the position indicator. In such a position input system, because the signals transmitted from the position indicator to the position detection device are comparatively weak, the sensitivity and precision of the position detector device may be reduced in an environment of intense electromagnetic noise, such as may be generated by the liquid crystal display device or other sources. As a countermeasure, the signals transmitted from the position detector device may be strengthened. However, strengthening of the signals is problematic inasmuch as power consumption by the position detector device is increased.
It has been proposed to incorporate a battery into the position indicator, so that the transmission of signals from the position detector device becomes unnecessary. Using such a method, strong signals can be transmitted from the position indicator with low power consumption.
However, the use of batteries can also raise problems. In the case of the above-described position indicator, replacing the battery is time consuming and troublesome. Also, if the intensity of signals transmitted from the position indicator is to be increased, power consumption is increased and battery depletion occurs in a short length of time, so that the batteries built into the position indicator may need to be replaced frequently, causing further inconvenience. In addition, the weight of a position indicator incorporating a battery is increased significantly, and there is the further problem that operating properties are severely degraded.
Recently, it has been known to provide position pointing devices with tuning circuits at both ends of their pen-like bodies. The tuning circuit at the first end is able to transmit written information, and the tuning circuit at the other or second end is able to transmit other information, such as the erasing of information. See Japanese Published Patent Application No. 8-96350. It has been proposed to provide such position pointing devices with built-in power supply units and oscillation units to increase the magnitude of transmission output, and thereby improve accuracy in detecting position. See Japanese Published Patent Application No. 10-214148.
However, if a position pointing device possesses a built-in power supply unit (i.e., a battery) and a plurality of oscillation units instead of the above-discussed tuning circuits, then power consumption of the built-in power supply unit is increased by a multiple equal to the number of oscillation units in the position pointing device, e.g., if the position pointing device contains two oscillation units, then power consumption is doubled. Accordingly, the time period during which the position pointing device may be operated prior to consumption of all of the power in the built-in power supply is lessened correspondingly. As a result, the battery must be replaced or recharged more frequently, inconveniencing the operator.